1. Field of Invention
The present invention relates to a liquid crystal display device and electronic equipment. More specifically, the present invention relates to a reflective or semitransmissive reflective liquid crystal display device having a reflective layer or a semitransmissive reflective layer and to electronic equipment using the liquid crystal display device.
2. Description of Related Art
Recently, reflective or semitransmissive reflective liquid crystal display devices have been proposed. These devices have a reflective layer which uses, for example, a metal thin film or a semitransmissive reflective layer which uses a material, such as a cholesteric liquid crystal. For example, Al and Ag having a high reflectivity are used as the metal thin film. In such a device, incident extraneous light, such as sunlight and luminous light, is reflected through a liquid crystal layer, and the liquid crystal layer is driven so as to create a reflective display.
The cholesteric liquid crystal can include liquid crystal molecules structurally arrayed as a periodic helix with a constant pitch, selectively reflects light with a wavelength corresponding to the pitch of the helix and transmits the other light. Such a device using a reflector plate having the cholesteric liquid crystal selectively reflects light with a specific wavelength and transmits the other light to create a semitransmissive reflective display.
These types of reflective or semitransmissive reflective liquid crystal display devices can each include a plurality of dot display domains separated by black matrices, and either one of the dot display domains is capable of displaying one of the light""s three primary colors. A trio of red, green and blue dots display domains forms a pixel. Each black matrix separating the dot display domains serves to create a black display in the formation zone and uses, for example, a resin shielding film containing a pigment.
When such a resin shielding film is used as the black matrix, the resin shielding film might transmit trace light, although it absorbs light. If the shielding film transmits the light, it may cause light leakage to thereby reduce contrast.
The present invention has been accomplished to solve the above problems, and an object of the present invention is to provide a liquid crystal display device that can reliably avoid color mixing between dot display domains at the boundary therebetween and can prevent or suppress decrease in contrast. Another object of the present invention is to provide electronic equipment using the liquid crystal display device.
To achieve the above objects, the present invention can provide a liquid crystal display device having a liquid crystal cell, the liquid crystal cell including a pair of substrates facing each other and a liquid crystal layer disposed between the pair of substrates. The liquid crystal display device can include a plurality of dot display domains separated by a boundary domain and disposed in a plane, a specific circularly polarized light introducing device that is capable of introducing circularly polarized light having a predetermined rotational direction between the pair of substrates, and a reflecting device that is capable of at least reflecting circularly polarized light, the reflecting device including a rotational direction controlling device that is capable of controlling the rotational direction of the circularly polarized light reflected in the dot display domains to differ from that reflected in the boundary domain.
In this device, when circularly polarized light having a predetermined rotational direction enters between the pair of substrates from the specific circularly polarized light introducing device and is reflected by the reflecting device, the circularly polarized light reflected in the dot display domains can have a rotational direction different from that reflected in the boundary domain. Accordingly, the circularly polarized light reflected in the dot display domains can exit from the specific circularly polarized light introducing device, and the circularly polarized light reflected in the boundary domain cannot exit from the specific circularly polarized light introducing device.
Specifically, the specific circularly polarized light introducing device can allow the circularly polarized light reflected in a dot display domain to exit to thereby create a bright display in the dot display domain and can allow the circularly polarized light reflected in the boundary domain not to exit to thereby create a dark display in the boundary domain. Accordingly, the device can use the domain capable of at least producing a bright display as a display domain (pixel domain) that contributes to display, and the domain capable of producing a dark display as a non-display domain that does not contribute to display, i.e., a black matrix. The rotational direction of the incident circularly polarized light in a dot display domain can be changed based on the orientation mode of the liquid crystal layer. By this configuration, a bright or dark display can freely be created in the dot display domain.
This configuration can be easily formed and is resistant to transmittance in the black matrix to prevent or suppress decrease in contrast due to light leakage. The contrast decreases due to transmittance in the black matrix in the following manner. In reflective display, for example, light transmitting the black matrix is reflected and contributes to a bright display. In semitransmissive reflective display, for example, light passing through the black matrix in transmissive display contributes to a bright display. Thus, the present invention can achieve a configuration that yields less decrease in contrast than a configuration using a resin shielding film as a black matrix in a liquid crystal display device which creates at least a reflective display. The term circularly polarized light as used herein also includes elliptically polarized light
More specifically, the reflecting device may include a first reflective layer capable of reflecting at least a part of circularly polarized light having a predetermined rotational direction and capable of allowing the circularly polarized light after reflection to have the same rotational direction as that before reflection, and a second reflective layer capable of at least reflecting circularly polarized light and capable of allowing the circularly polarized light after reflection to have a different rotational direction from that before reflection, in which the first reflective layer and the second reflective layer are disposed in either of the dot display domains and the boundary domain, respectively.
In this device, the first reflective layer is capable of allowing the circularly polarized light after reflection to have the same rotational direction as that before reflection and the second reflective layer is capable of allowing the circularly polarized light after reflection to have a different rotational direction from that before reflection. Thus, a dark display as a black matrix can reliably be created in the boundary domain. When the first reflective layer structurally reflects a part of and transmits the other part of circularly polarized light having a predetermined rotational direction, the first reflective layer serves as a semitransmissive reflective layer. For example, by allowing the rotational direction of incident circularly polarized light in a domain where the first reflective layer is disposed to vary depending on the orientation mode of the liquid crystal layer, a reflective or transmissive display can be optionally created in the dot display domain. In this case, the second reflective layer plays a role as a black matrix in reflective display as above. In contrast, a transmissive display can be created by allowing the first reflective layer to transmit light from a light source (hereinafter referred to as internal light) that can enter in a direction different from that in the reflective display. The second reflective layer in this case reflects the internal light that can enter in a direction different from that in the reflective display and can play a role as a black matrix. Accordingly, the device according to the present invention can create a high-contrast display both in the reflective and the transmissive displays. In this connection, by controlling the rotational direction of the circularly polarized light coming into the first reflective layer based on the driving mode of the liquid crystal layer in a dot display domain, a bright or dark display can be created in the dot display domain.
The device may also have a configuration, in which the first reflective layer is arranged across the dot display domain and the boundary domain, the second reflective layer is arranged only in the boundary domain. Further, the first reflective layer can be arranged between the liquid crystal layer and one of the pair of substrates and at least serves as a reflecting means in the dot display domains, and the second reflective layer can be arranged closer to the other substrate of the pair of substrates than the first reflective layer and serves as a reflecting means in the boundary domain.
In the above device, for example, the second reflective layer can prevent the circularly polarized light from entering at the first reflective layer in the boundary domain and can prevent an desired display caused by the reflection in the first reflective layer in the boundary domain. Accordingly, the device can create a reflective display reflected by the first reflective layer alone in the dot display domain and a reflective display reflected by the second reflective layer alone in the boundary domain. Thus, the device can create high-contrast reflective display.
The first reflective layer can mainly include a cholesteric liquid crystal. The cholesteric liquid crystal selectively reflects light with a wavelength corresponding to the pitch of its helix and transmits the other light. In addition, circularly polarized light reflected by the cholesteric liquid crystal has a different rotational direction from that before reflection. Accordingly, such a cholesteric liquid crystal can be used as the first reflective layer in the present invention.
The second reflective layer can mainly include one or more metal films selected from Cr, Ta, Ag, and Al. Such metal films can highly shield the internal light, lead to no depolarization and enables the circularly polarized light after reflection to have a different rotational direction from that before reflection and are suitable as the second reflective layer in the present invention. In stead of metal films, for example, a dielectric mirror mainly including an inorganic oxide can be used as the second reflective layer.
The liquid crystal display device of the present invention may further include a first circularly polarized light introducing device that introduces circularly polarized light through one of the pair of substrates into the liquid crystal layer and serving as the specific circularly polarized light introducing device, and a second circularly polarized light introducing device that introduces circularly polarized light through the other of the pair of substrates and serving as the specific circularly polarized light introducing device. The circularly polarized light described above has the same rotational direction as the circularly polarized light from the one of the pair of substrates. Further, the invention can include a luminaire for introducing light through the other substrate into the liquid crystal cell, in which the liquid crystal layer reverses the polarity of incoming circularly polarized light in one of the case with the application of a selective electric field and the case without the application of a selective electric field and does not in the other case.
By this configuration, the luminaire arranged close to the other substrate enables a semitransmissive reflective display in a domain in which the first reflective layer is arranged, and the second reflective layer can also play a role as a black matrix in the semitransmissive reflective display to create a high-contrast display.
The specific circularly polarized light introducing device may have a polarizing plate capable of transmitting linearly polarized light in one direction, and a wave plate capable of converting the linearly polarized light passed through the polarizing plate into circularly polarized light. In this case, the polarizing plate can yield linearly polarized light, the linearly polarized light passes through the wave plate to yield circularly polarized light. By equalizing the polarizing axes in the polarizing plates and the phase differences of the wave plates in the pair of substrates, circularly polarized light having the same rotational direction can be obtained in the two substrates.
In addition, the present invention provides electronic equipment including the liquid crystal display device having the above configuration. This configuration can provide electronic equipment having a high-contrast display unit.
The term mainly includes an ingredient as used herein can be used to describe that the ingredient is contained at the highest content among constitutive ingredients in a unit in question.